The video, from Modern Markets Initiative, also inadvertently spelled out some of the negative side effects, too.

Toward the end of the video, Mark Gorton, the founder of Tower Research Capital, made the following statement (emphasis ours):

The most positive development on Wall Street in the last twenty years is the advent of electronic trading. You used to have a lot of very highly paid people on Wall Street. A lot of those jobs have been automated away. For average investors around the country, they should be very happy that they are saving money thanks to the new automated markets.

I am pretty sure the Wall Streeters who have had their jobs automated away do not consider electronic trading the most positive development on Wall Street. In fact, I am pretty sure they are pretty upset about it. I have had emails from out-of-work traders saying as much.

Now, this isn't a negative side effect of HFTs so much as the technology that has allowed them to prosper.

Electronic markets also reduce the need for human labor, undermining the requirements for individual desktop software, terminals, and other graphical-user-interface products. This development increases the relevance of other layers in the technology stack, such as security, data centers, communication protocols, and physical networks.

Elsewhere in the MMI video, Jason Carroll, a managing director at Hudson River Trading, pointed out that the market was ripe for this kind of a technological advancement (emphasis ours):

We had a situation where people were literally yelling prices across the floor and making decisions in their heads about what they wanted to buy, how much they wanted to buy, what price they wanted to buy. The consequence was that the cost was relatively high. US equity markets were ready for a technological revolution.